In application Ser. No. 64,180 of Brouwer et al, filed Aug. 6, 1979, commonly assigned herewith, there is disclosed and claimed a loom and weaving method embodying an air weft insertion system of the type generally defined above in which a pulse of pressurized air of abbreviated duration relative to the duration of the overall weaving cycle of the loom is delivered via a valve from a constantly pressurized air supply chamber to the throat of the weft insertion nozzle directed toward the shed of the loom, which throat is preferably contoured so as to expel such air from its exit opening at a supersonic velocity, the leading end of the weft yarn to be inserted from a weft supply preferably by means of a delivery unit, being disposed within the throat of this nozzle for contact with the air stream passing therethrough and projection thereby into and across the shed of the loom to the opposite side thereof.
This system imposes special and demanding requirements upon the control of the actuation, i.e. opening and closing, of the nozzle valve in order to achieve the air pulse characteristics emitted by the nozzle, including brief duration as well as velocity, needed to impart substantial thrust to the yarn, and in a companion application Ser. No. 64,395 of Brouwer et al, also filed Aug. 6, 1979 and commonly assigned herewith, there is disclosed and claimed a preferred control system for effecting the opening and closing of the nozzle in a manner achieving the required pulse characteristics.
The preferred control system of application Ser. No. 64,395 utilizes a flexible diaphragm as the valve for alternately closing the exit opening of the pressurized air supply chamber and then opening to place the chamber exit opening into communication with the throat passageway of the nozzle wherein the leading weft yarn end is already situated. Advantageously, the air supply chamber is developed as an annular envelope around the nozzle throat passageway so that the exit opening of the chamber is annular and is coterminous and coaxial with an annular inlet opening of the nozzle passageway so that both such openings can be isolated by means of a common diaphragm valve and placed in communication or joined together when the diaphragm opens.
Movement of the diaphragm valve to open and close the supply opening is determined by the application to and release of a control pressure to and from the face of thee diaphragm opposite that face closing the supply chamber opening and preferably nozzle throat openings, as well as such pressure being preferably applied to an annular area of the opposite diaphragm face which area is defined by means of a pilot chamber disposed proximate the opposite diaphragm face. The pilot chamber is alternately placed in communication with a source of pilot or control pressure and the ambient atmosphere, to cause closing and opening of the diaphragm valve, by means of a spool servo valve arrangement which can take several different forms but in all cases incorporates a coordinated pair of rotating spool valves contoured with operative lands and grooves, one governing the pressurization of the pilot chamber and the other governing the de-pressurization or venting of the pilot chamber so that the closing and opening of the diaphragm valve can be carried out independently from a control standpoint. The initial starting angular positions of the spool valves are adjustable relative to one another, thereby permitting direct adjustment of the length of time correspondng to the difference in the starting spool positions the diaphragm valve is allowed to remain open during each cycle of spool rotation.
While the nozzle actuating control system of application Ser. No. 65,395 has been found to work effectively in practice, there is room for improvement. On the other hand, the diaphragm valve which is made of durable heavy rubberized fabric or the like clamped along both its center region and external margins with an intermediate annular flexible region exhibits an operating life in the order of several millions of cycles; and while this durability is certainly high by ordinary mechanical standards, a loom weaving at the rate of 400 picks per minute passes through more than one million cycles during each 48-hour week of a single shift of operation. Consequently, the diaphragm of the above control unit may require replacement after several weeks or at most a few months of use under normal conditions.
On the other hand, the construction of the rotary valve array, while decidedly advantageous in the light of the prior art nozzle control concepts, is complicated especially as regards the precise contouring of the peripheral surfaces of the respective spool valves to form the arrangement of lands and recesses needed to control the flow of pressurized pilot air in both directions therethrough and to impart balancing pressure forces to offset the main air flow effect and avoid premature wear.